The presently disclosed embodiments relate in general to electrostatography comprising improved features in the flexible imaging member that enhance function when used in the electrostatographic imaging system. These embodiments pertain, more particularly, to two ground strip layer design variances to respectively meet two specific flexible electrostatographic imaging member belts need for dynamic belt cyclic motion quality improvement and service life extension in electrostatography.
Flexible electrostatographic imaging members are known in the art. Typical flexible electrostatographic imaging members include (1) flexible electrophotographic imaging members or flexible photoreceptors for electrophotographic imaging systems and (2) flexible electroreceptors such as flexible ionographic imaging members for electrographic imaging systems. Generally, these imaging members comprise at least a flexible supporting substrate and at least one imaging layer comprising a thermoplastic polymeric matrix material coated over the flexible substrate. In a flexible electrophotographic imaging member or photoreceptor, the photoconductive imaging layer may comprise only a single photoconductive layer or multiple of layers such as a combination of a charge generating layer and one or more charge transport layer(s). Whereas in a flexible electroreceptor, the imaging layer is a dielectric imaging layer. For all these flexible electrophotographic imaging members, they can have a number of distinctively different configurations; for example, they can be in the form, such as a flexible scroll or a flexible belt each containing a flexible substrate.
Even though the flexible electrostagraphic imaging members of the present embodiments relate to both electrophotographic imaging members (or photoreceptors) and ionographic imaging members (electroreceptors) in any respective flexible configuration, for reason of simplicity, all disclosed embodiments detailed hereinafter will be focused and primarily represented by negatively charged flexible electrophotographic imaging member belts prepared to consist of two structurally distinctive designs, for use in electrophotography. The two designs are for a full imaging member belt structure and a structurally simplified imaging belt.
For a full imaging member belt structure, the flexible electrophotographic imaging member belts are generally prepared in a seamed or seamless belt configuration. Flexible electrophotographic imaging member seamed belts are typically fabricated from a sheet which is cut from a flexible imaging member web stock. The sheets are generally rectangular in shape. The edges may be of the same length or one pair of parallel edges may be longer than the other pair of parallel edges. The sheets are formed into a belt by joining overlapping opposite marginal end regions of the sheet. A seam is typically produced in the overlapping marginal end regions at the point of joining. Joining may be effected by any suitable means. Typical joining techniques include welding (including ultrasonic), gluing, taping, pressure heat fusing, and the like. Ultrasonic welding is generally the more desirable method of joining because it is rapid, clean (no solvents) and produces a thin and narrow seam. In addition, ultrasonic welding is more desirable because it causes generation of heat at the contiguous overlapping end marginal regions of the sheet to maximize melting of one or more layers to produce a strong fusion bonded seam. The prepared flexible imaging member seamed belt is mounted over and encircled around a belt support module comprising numbers of belt support rollers and backer bars ready for electrophotographic imaging function. The flexible electrophotographic imaging member seamed belt is imaged by uniformly depositing an electrostatic charge on the imaging surface of the electrophotographic imaging member and then exposing the imaging member to a pattern of activating electromagnetic radiation, such as light, which selectively dissipates the charge in the illuminated areas of the imaging member while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking toner particles on the imaging member surface. The resulting visible toner image can then be transferred to a suitable receiving member or substrate such as paper. Therefore, under these normal machine operation conditions in the field, the flexible imaging member seamed belt is in dynamic fatigued cyclic motion during electrophotographic image printing processes.
In a fully structured imaging member belt design, the charge transport layer and its adjacent ground strip layer are the two top outermost layers that are constantly exposed to the environment contaminants as well as machine subsystems mechanical interactions such as cleaning device actions during electrophotographic imaging processes. Likewise, the anticurl back coating, as the bottom outermost exposed layer, is also subjected to belt support module components mechanical action under dynamic belt cycling function condition. As a consequence, these interactions have been seen to cause and exacerbate the early development of charge transport layer material failures in the belt, causing copy printout defects to prematurely cut short its service life prior to reaching the intended belt life target. Moreover, the bottom outermost exposed the anticurl back coating is constantly subjected to belt support rollers and backer bars mechanical interactions which promotes on-set of premature anticurl back coating wear and abrasion streaking failures.
Since a typical flexible electrophotographic imaging member exhibits spontaneous upward imaging member curling after completion of solution coating the top outermost exposed charge transport layer, an anticurl back coating is applied to the back side of the flexible substrate support to counteract/balance the curl and provide the desirable imaging member flatness.
A large number of the current flexible electrophotographic imaging member belts, that are used in a typical negatively charged xerographic imaging machine design, are multilayered photoreceptor belts comprising a flexible substrate support, an electrically conductive layer, an optional charge blocking layer, an optional adhesive layer, a charge generating layer, a top outermost charge transport layer having a co-coated ground strip layer (for electrical connectivity to the conductive layer) applied adjacent to the charge transport layer and at one edge of the belt, and an anticurl back coating at the opposite side of the substrate support. Since these flexible electrophotographic imaging member belts always exhibit upward curling after completing the solution application coating process of a charge transport layer and co-coated ground strip layer, the anticurl back coating is needed and applied on the back side of the flexible substrate support, opposite from the electrically active layers, to balance/control the curl and render imaging member belt flatness.
Although the application of an anticurl back coating is effective to counter and remove the curl, nonetheless the prepared flat imaging member web does have charge transport layer tension build-up creating an internal strain of about 0.27% in the charge transport layer and also in the ground strip layer as well. The magnitude of this charge transport layer internal strain build-up is very undesirable, because it is additive to the induced bending strain of an imaging member belt as the belt dynamically bends and flexes over each belt support roller during dynamic fatigue belt cyclic motion under a normal machine electrophotographic imaging function condition in the field. The summation of the internal strain and the cumulative fatigue bending strain sustained in the charge transport layer has been found to exacerbate the early onset of charge transport layer cracking, preventing the belt to reach its targeted functional imaging life. Moreover, employing an anticurl backing coating adds to the total belt thickness and increases charge transport layer bending strain which then exacerbates the early onset of belt cycling fatigue charge transport layer cracking failure. The cracks formed in the charge transport layer as a result of dynamic belt fatiguing are found to manifest themselves into copy print-out defects, which adversely affect the image quality printout on the receiving paper.
Various belt function deficiencies have also been observed in these common anticurl back coating formulations used in a typical conventional imaging member belt, such as the anticurl back coating does not always providing satisfying dynamic imaging member belt performance result under a normal machine functioning condition; for example, exhibition of anticurl back coating wear and its propensity to cause electrostatic charging-up are the frequently seen problems to prematurely cut short the service life of a belt and requires its frequent costly replacement in the field. Anticurl back coating wear under the normal imaging member belt machine operational conditions reduces the anticurl back coating thickness, causing the loss of its ability to fully counteract the curl as reflected in exhibition of gradual imaging member belt curling up in the field. Curling, caused by the internal strain in the charge transport layer and the ground strip layer, is undesirable during photoreceptor belt function, because different segments of the imaging surface of the photoconductive member are located at different distances from charging devices, causing non-uniform charging. In addition, developer applicators and the like, during the electrophotographic imaging process, may all adversely affect the quality of the ultimate developed images. For example, non-uniform charging distances can manifest as variations in high background deposits during development of electrostatic latent images near the edges of paper. Since the anticurl back coating is an outermost exposed backing layer and has high surface contact friction when it slides over the machine subsystems of belt support module, such as rollers, stationary belt guiding components, and backer bars, during dynamic belt cyclic function, these mechanical sliding interactions against the belt support module components not only exacerbate anticurl back coating wear, it does also cause the relatively rapid wearing away of the anticurl back coating produce debris which scatters and deposits on critical machine components such as lenses, corona charging devices and the like, thereby adversely affecting machine performance. Moreover, anticurl back coating abrasion/scratch damage does also produce unbalance forces generation between the charge transport layer and the anticurl back coating to cause micro belt ripples formation during electrophotographic imaging processes, resulting in streak line print defects in output copies to deleteriously impact image printout quality and shorten the imaging member belt functional life.
High contact friction of the anticurl back coating against machine subsystems is further seen to cause the development of electrostatic charge built-up problem. In other machines the electrostatic charge builds up due to contact friction between the anti-curl layer and the backer bars increases the friction and thus requires higher torque to pull the belts. In full color machines with 10 pitches this can be extremely high due to large number of backer bars used. At times, one has to use two drive rollers rather than one which are to be coordinated electronically precisely to keep any possibility of sagging. Static charge built-up in anticurl back coating increases belt drive torque, in some instances, has also been found to result in absolute belt stalling. In other cases, the electrostatic charge build up can be so high as to cause sparking.
Another problem, encountered in the conventional belt photoreceptors using a bisphenol A polycarbonate anticurl back coating that are extensively cycled in precision electrophotographic imaging machines utilizing belt supporting backer bars, is an audible squeaky sound generated due to high contact friction interaction between the anticurl back coating and the backer bars. Further, cumulative deposition of anticurl back coating wear debris onto the backer bars may give rise to undesirable defect print marks formed on copies because each debris deposit become a surface protrusion point on the backer bar and locally forces the imaging member belt upwardly to interferes with the toner image development process.
Thus, electrophotographic imaging member belts comprising a supporting substrate, having a conductive surface on one side, coated over with at least one photoconductive layer (such as the outermost charge transport layer) having a co-coated adjacent ground strip layer at one edge of the belt, and the application on the other side of the supporting substrate with a conventional anticurl back coating that does exhibit deficiencies which are undesirable in advanced automatic, cyclic electrophotographic imaging copiers, duplicators, and printers. While the above mentioned electrophotographic imaging member belts may be suitable or limited for their intended purposes, further improvement on these imaging member belts are needed. For example, there continues to be the need for improvements in such systems, particularly for an imaging member belt that has sufficiently flatness, superb wear resistance, nil or no wear debris, ease of belt drive, and eliminates electrostatic charge build-up problem, even in larger printing apparatuses. With many of above mentioned shortcomings and problems associated with electrophotographic imaging member belts having an anticurl back coating now understood, therefore there is a need to resolve these issues through the development of a methodology for fabricating imaging member belts that produce improve function and meet future machine imaging member belt life extension need.
More recently, to overcome the shortcomings associated with the anticurl back coating function, flexible electrophotographic imaging member belts have been successfully re-designed to give a structurally simplified configuration to give flatness without the need of an anticurl back coating. In these structurally simplified imaging belts, incorporation of a high boiler liquid plasticizer into the top outermost exposed charge transport layer of the negatively charge imaging member belt helps provide the reduction/elimination of dimensional contraction differential between the charge transport layer and the flexible substrate support which relieves the internal strain build-up in the charge transport layer to suppress the curl-up tension stress. Similarly, the ground strip layer likewise incorporates a plasticizer as described in the charge transport layer to render the resulting imaging member with desired flatness.
Conventional photoreceptors are disclosed in the following patents, a number of which describe the presence of light scattering particles in the undercoat layers: Yu, U.S. Pat. No. 5,660,961; Yu, U.S. Pat. No. 5,215,839; and Katayama et al., U.S. Pat. No. 5,958,638. The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.”
Horgan et al., U.S. Pat. No. 4,664,995 issued on May 12, 1987, discloses an electrostatographic imaging member comprising at least one imaging layer capable of retaining an electrostatic latent image, a supporting substrate layer having an electrical conductive surface, and an electrically conductive ground strip layer adjacent the electrostographic imaging layer and in electrical contact with the electrical conductive layer, the electrical conductive ground strip layer comprising a film forming binder, conductive particles and crystalline particles dispersion in the film forming binder and a reaction product of a bifunctional chemical coupling agent with both the film forming binder and the crystalline particles. The imaging member may be employed in an electrostatographic imaging process.
Yu, U.S. Pat. No. 6,183,921 issued on Feb. 6, 2001, discloses a crack resistant and curl-free electrophotographic imaging member design which includes a charge transport layer comprising an active charge transporting polymeric tetraaryl-substituted biphenyldiamine, and a plasticizer.
In U.S. Pat. No. 7,413,835 issued on Aug. 19, 2008, there is disclosed an electrophotographic imaging member having a thermoplastic charge transport layer, a polycarbonate polymer binder, a particulate dispersion, and a high boiler compatible liquid. The disclosed charge transport layer exhibits enhanced wear resistance, excellent photoelectrical properties, and good print quality.
In U.S. patent application Ser. No. 12/762,257 to R. Yu et al., entitled Imaging Members Having Stress/Strain Free Layers, discloses embodiments comprising improved features in the flexible imaging member that enhance function when used in the electrostatographic imaging system. These embodiments pertain, more particularly, to a structurally simplified curl-free flexible electrostatographic imaging member belt containing a stress/strain free ground strip layer and stress/strain free imaging layer(s) to improve dynamic belt cyclic motion quality and extend service life.
All the above-disclosed prior art electrophotographic imaging members belts, however, either having a full imaging member structure that includes an anticurl back coating or a structurally simplified curl-free design that requires no anticurl back coating, do each comprise a top outermost exposed ground strip layer (co-coated adjacent to the charge transport layer to effect electrical connectivity between the photo-electrically active layers in the members) that exhibits deficiencies and shortfalls which are undesirable in advanced automatic, cyclic electrophotographic imaging copiers, duplicators, and printers and therefore needs improvement.